This invention concerns electrically conducting drain members useable to ground sleeves providing shielding from electromagnetic and radio frequency interference.
Electromagnetic interference (EMI) and radio frequency interference (RFI) pose a potential problem preventing the proper functioning of electronic components caused by interference due to inductive coupling between nearby electrical conductors carrying time varying currents or conductors subject to propagating electromagnetic waves. For example, electrical currents in conductors associated with the ignition system or the electrical power system in an automobile may induce spurious signals in various electronic components, such as an electronic module which controls the functioning of the engine or the braking system. Such spurious signals could have disastrous consequences and cause the control modules to malfunction or respond as if the spurious induced signals represented a real condition, potentially causing a loss of control of the vehicle.
Similarly, inductive coupling between electrical wiring and the lines carrying data in a computer network or other communication system may have a corrupting effect on the data being transmitted over the network.
The adverse effects of EMI and RFI are effectively eliminated by proper shielding and grounding of EMI sensitive components. For example, wires carrying control signals which may be subject to unwanted induced interference may be shielded by using a protective sleeve as described in U.S. Pat. No. 4,684,762 to Gladfelter, wherein the sleeve is formed of electrically conductive and non-conductive interlaced yarns (woven, braided or knitted), the conductive yarns being grounded via a drain wire interlaced with the yarns during manufacture of the sleeve, the drain wire being in electrical contact with the conducting yarns.
While such RFI/EMI sleeving is effective at eliminating electrical interference, the sleeving is difficult to properly ground. The sleeve is first cut to a length which is longer than necessary to merely cover the wires to be shielded in order to provide a free length of drain wire for connecting to ground. The free length of drain wire is then formed by cutting away a portion of the sleeve around the drain wire. The sleeve is positioned around the wires to be shielded and the free length of drain wire is connected to ground. This process is wasteful of sleeving and time consuming for the installer, who must cut more sleeve than needed then cut away some of the sleeve without damaging the drain wire to expose it for connection to ground. There is clearly a need for improved RFI/EMI shielding which is less wasteful and may be installed with less effort in a shorter period of time.
The invention concerns a shield for protecting an elongate electrical conductor against radio frequency and electromagnetic interference. In its preferred embodiment, the shield comprises an elongated sleeve having a central space for receiving the conductor. The sleeve is formed of a plurality of flexible and resilient first filamentary members interlaced together. The plurality of first filamentary members includes at least some electrically conducting filamentary members. A pair of filamentary drain members are oriented substantially lengthwise along the sleeve and are interlaced with the first filamentary members. The drain members are flexible, electrically conductive and are in electrical contact with one another and the electrically conducting filamentary members comprising the plurality of first filamentary members. One of the drain members has a lengthwise portion which is extendible away from the sleeve and connectable to an electrical ground for grounding the sleeve.
Preferably, one drain member is interlaced with the first filamentary members at a plurality of discrete regions of attachment arranged in spaced relation lengthwise along the sleeve. The one drain member thus comprises a plurality of segments which float along a surface of the sleeve, one of the segments being positioned between each of the discrete regions of attachment. The one drain member is severable at one of the segments and is thereby extendible away from the sleeve for connection to the electrical ground. The segments of the drain member which float along the surface are preferably longer than the regions of attachment.
The shield according to the invention also comprises a seam extending lengthwise along the sleeve to provide access to the central space. The seam is defined by a pair of free edges which extend lengthwise along the sleeve. Biasing means are located within the sleeve for resiliently biasing the edges into overlapping relation with one another to close the seam. One of the edges is preferably positioned to overlap the other, and the drain members are positioned on the sleeve so as to be covered by the one edge.
Preferably, the drain members comprise stranded copper wire and the first filamentary members are interlaced by weaving, the drain members being interwoven with the first filamentary members. For effective RFI/EMI shielding, the conducting filamentary members comprise between about 10% and about 80% of the sleeve by weight.
It is an object of the invention to provide an RFI/EMI shield which is easily groundable.
It is another object of the invention to provide an RFI/EMI shield in the form of a sleeve adapted for elongate conductors.
It is again another object of the invention to provide an RFI/EMI shield having drain members which are extendible from the shield and attachable to an electrical ground.
These and other objects and advantages of the invention will become apparent upon consideration of the following drawings and description of preferred and alternate embodiments.